Radio communication system



June 28, 1938.

F. G. KEAR ET AL RADIO- COMMUNICATION SYSTEM Filed Aug. 5, 1933 -crB-C,

2 Sheets-Sheet 1 f m 9 Q mam kw 5610K flar' Gamer A. flay/es ////@M M 0r/0/7 June 28, 1938. F. G. KEAR ET AL RADIO COMMUNICATION SYSTEM Filed Aug. 3, 1933 2 Sheets-Sheet 2 500M L. Dav/es Wil/iam /lflr w- Patented June 28, 1938 UNITED STATES PATENT OFFICE RADIO COMMUNICATION SYSTEM poration of Delaware Application August 3,

3 Claims.

This invention relates to systems for communication by radio and, more particularly, to such a system which is especially designed for communication within a limited area.

An object of the invention is to provide a system of radio communication which will be particularly adapted to enable the communication of commands or orders from a central point to persons who may move about within a restricted area, and in the use of which effective reception will be possible only within such restricted area.

Another object is to provide a system of limited range radio communication in which transmission is efiected at carrier frequencies, whereby the disadvantages and difficulties of audio frequency transmission or systems employing pure inductive methods are obviated. In carrying the system into effect an antenna array having poor radiation characteristics but a strong local or induction field is employed, which local or induction field may be employed for communication purposes. By this means the advantages of transmission at carrier frequencies are obtained, as well as the limited range features of communication through the inductive field. It will also be seen that such a communication system will cause no interference to radio reception by receivers other than those operating within the restricted area of limited range transmission.

A further object of the invention is to provide a system of limited range communication for a restricted area which will have such characteristics that a low-sensitivity, low-frequency receiving apparatus, which will be immune to static or other interfering signals, may be employed therewith.

Other objects and features of novelty will be apparent from the following description and drawings, it being expressly understood, however, that the invention is in no way limited by such description and drawings or otherwise than by the appended claims.

Referring to the drawings, in which similar reference numerals refer to like parts: h

Fig. 1 is a diagrammatic view of a suitable transmission system which may be employed in practicing the invention;

Fig. 2 is a diagrammatic view of a suitable receiving system which may be employed;

Fig. 3 is a view showing the adaptation of the antenna to the deck of a ship; and

Fig. 4 is a detail view showing one method by which the antenna wires may be disposed below the surface of a floor or deck.

The invention contemplates the provision of a 1932, Serial No. 683,518

radio transmission system capable of supplying an antenna with audio-frequencies through the medium of a low-frequency carrier wave. Such a transmitter is illustrated diagrammatically in Fig. 1 wherein is disclosed a transmission system 5 comprising an oscillator I, with three stages of amplification being provided by the buffer amplifying tube 2, the modulation amplifying tube 3, and the power amplifier 4. A speech input means 5, such as a telephone, is provided and the 10 same, in cooperation with the audio-frequency modulator tube 20, modulates the plate current of the amplifier 3, thereby supplying to the antenna through amplifier i and transformer 6 a low-frequency carrier wave modulated by audio- 5 frequencies. It will be understood that the transmission system described is for the purpose of illustration only and that any suitable transmitter capable of supplying to the antenna a low= frequency carrier wave modulated by audioefre- 20 quencies may be employed. Any suitable number of stages of amplification may. also be employed, as the specific transmitting system forms no part of the invention, so long as the proper wave characteristics are supplied thereby.

The antenna, to which the above described transmission system supplies the modulated lowfrequency carrier wave, is adapted according to the invention to be disposed in a horizontal plane adjacent to or within the flooring of a restricted 30 area of any kind.- such as a factory, or adjacent to or within the deck of a ship on which the transmission system may be carried. In Figs.

3 and 4 there is disclosed the preferred antenna array and the same is illustrated as being mount- 35 ed on or within the deck of a ship 8, such as an aircraft carrier. Disposed in a plane parallel to the deck I of the ship 8 and preferably closely adjacent thereto are two sets of antenna wires 9, III, the same being connected in parallel as 40 clearly disclosed in Fig. 3 in order to reduce the resistance of the antenna system. Referring particularly to Fig. 3 it will be seen that the secondary of transformer 6 is connected to the antenna element 9 which is then disposed laterally 45 of the deck in one direction, then longitudinally of the deck for a suitable distance, then laterally of the deck, and in this manner is made to traverse the entire length of the deck, whereupon it is reversed in direction'and brought back in the same manner and connected to the other-terminal of the secondary of transformer 6. The second radiating element I0 is disposed parallel to and closely adjacent the element 9 throughout its length and is connected in parallel thereto by means of the wires ll, l2. By means of this arrangement a duplicate antenna system is provided having a low resistance due to the connection of the duplicate systems in parallel. It will be seen that the antenna 9, due to its arrangement as described above, provides a series of connected loops along the deck, such loops being designated by the letter A. The current flow in the loops A is shown by the arrows on antenna wire 9 in Fig. 3 of the drawings. The antenna wire l0, due to its arrangement as described above, also provides a series of connected loops B the sides of which are spaced from the sides of loops A. The current fiow in loops B is shown by the arrows on antenna Iii in Fig. 3. The nature of the radiation from a loop antenna is well-known, and in the present embodiment of the invention it will be apparent that radiation from the loops A and B, disposed adjacent the deck of a ship or adjacent the 'fiooring of a restricted area, will be polarized horizontally, i. e., in the plane of the loops.

One way in which the radiating elements may be disposed adjacent the deck is illustrated in Fig. 4, in which is disclosed the deck planking I3, it, having the calking material l5, l6, l1 disposed therebetween. Embedded in adjacent strips of calking material, as disclosed in Fig. 4, are laterally-extending portions of the radiating elements 9, it, the same being preferably completely embedded in the calking to prevent injury to the wires. It will be observed that whereas antenna wires are disposed within the adjacent calking strips l6 and I7, no wire is disposed within the calking strip 55. This is due to the fact that the distance between adjacent lateral portions of the same wire of the antenna array is preferably chosen as many times the width of the usual deck planking and is usually several feet. However, the distance between the two separate parallel radiating elements 9, I0 is very small at all points and the disposal of these wires in adjacent calking strips provides approximately the correct spacing. It is to be understood that the invention is not in any way limited to any specific spacing distance between parallel portions of the same antenna wire, or to any specific spacing distance between the separate antenna wires, but that any spacing which will give the desired result of reducing the radiated field to a minimum may be employed. While any suitable low-sensitivity, low-freuency receiving apparatus may be employed with the system so far described, it is preferred that a receiving set not employing vacuum tubes be employed in order to reduce the weight of the receiving set, as it is intended that the same be carried by a person moving about the deck.

or other area blanketed by the antenna. Accordingly, it is proposed to provide a receiving set which will be responsive to the induction field set up by the antenna disposed adjacent the deck as heretofore described. Such a receiving set is illustrated in Fig. 2 wherein is disclosed a loop of wire l8 which may be so assembled that it may be slung over the shoulder or otherwise suitably disposed, and which acts as a pick-up device. The receiving apparatus itself comprises an inductance coil 59, both the pick-up loop and the inductance being shunted by a variable capacity it, a metallic rectifier 2i and a head-set 22. Al-

though other receiving apparatus may be employed, it has been found that that disclosed provides satisfactory means for detecting the induction field set up by the deck-carried antenna;

From the above description it will be apparent that the described system of communication provides a transmitting system which supplies the antenna with voice frequencies through the medium of a low frequency carrier. It has been found that a carrier frequency of ten to sixty kilocycles provides the most satisfactory results. Due to the arrangement and disposition of the radiating elements in the antenna array it will be observed that the current in adjacent element flows in opposite directions and that consequently the radiated energy is very small. Further the fact that the antenna radiation is polarized horizontally makes the propagation of the radiated field along the surface of the water, or in the plane of the surface in or adjacent which the antenna is disposed, practically zero. Directly over the deck or other area covered by the antenna the radiated field is also practically zero, due to the directive nature of the antenna array. Consequently only a narrow cone between the extension of the plane of the deck and the vertical extension of the boundaries of the area covered by the antenna receives any radiation whatever. The effective field of the antenna is therefore very limited and may be said to be limited to the extent of the induction field thereof. Due to the characteristics of the inductive field of the antennas, voltages induced in the pick-up loop of the receiving apparatus will be entirely independent of the position of the receivingloop over the area covered by the antenna array.

The low-sensitivity, low-frequency portable receiving apparatus described and illustrated is so designed as to be sensitive to the inductive field set up by the antenna array embedded in the deck or flooring. Due to the low sensitivity of the receivers, which is permissible because of their sensitivity to the closely-adjacent inductive field, such receivers will be immune to static or other interfering signals, and should be unaffected by simultaneous radio transmissions from other sources.

It will be seen from the above that we have provided a limited range communication system by employing the inductive portion of the field set up by the antenna, and that by our disposition and arrangement of the antenna array we have successfully eliminated the greater part of the radiated field, whereby communication by means of our system may be restricted to a localized area.

While one modification of our invention has been illustrated and described in the present application, it will be apparent to those skilled in the art that modifications and changes may be made therein without departing in any way from the spirit of the invention, for the limits of which reference must be had to the appended claims.

What is claimed is:

1. An antenna array for a limited range radio communication system for a restricted area having a fioor surface formed of a plurality of substantially abutting members, comprising a radiating element having a portion disposed between adjacent members.

2. An antenna array for a limited range radio communication system for a restricted area having a fioor surface formed of substantially abutting fioor members, comprising a radiating element having a portion thereof disposed longitudinally of and between adjacent fioor members and another portion thereof extending laterally of said floor members, and a second radiating element paralleling said first-named element and adjacent floor members and another portion disbeing electrically connected in parallel thereto. posed in the plane of said floor members and 3. An antenna array for a limited range radio being arranged transversely to said floor memcommunication system for a restricted area havbets.

5 ing a floor surface formed of substantially abut- FRANK G. KEAR.

ting floor members. comprising a wire having a GOMER L. DAVIES. portion disposed longitudinally of and between WM.- H. OR'I'ON. 

